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National Information |
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Superfund Program
Arsenic Trioxide
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Site Type: Deleted NPL |
Site Status & Updates
EPA completed a third five-year review of the site in September 2008. Remedial actions were taken at the site to address arsenic concentrations in ground water, which serves as the primary drinking water source in the region. The occurrence of arsenic in ground water is attributed to both the historical use of arsenic-based grasshopper bait and naturally occurring sources.The five-year review was in response to the recently finalized Arsenic Rule, which lowered the Safe Drinking Water Act Maximum Contaminant Level for arsenic from 0.05 mg/L to 0.01 mg/L. Treatment of arsenic-contaminated ground water to provide drinking water is a key component of the remedy.
The remedy is operating consistent with the requirements of the Record of Decision but is no longer protective of human health and the environment because of existing water treatment capacities and the number of rural users not on public water supply.
EPA is working with North Dakota to ensure that the area's residents have safe drinking water.
Site Description
The Arsenic Trioxide site is located in southeastern North Dakota. It covers approximately 20 townships (about 568 square miles) encompassing portions of Richland, Ransom, and Sargent counties. The site area is sparsely populated farmland with a few small towns, including Lidgerwood, Wyndmere, Milnor and Hankinson. The site topography is primarily low rolling hills and flat plains. Ground water aquifer systems include shallow glacial drift aquifers approximately three to 150 feet deep and the Dakota Sandstone aquifer approximately 200 to 1,000 feet deep. Ground water with elevated arsenic levels appears to be limited to the upper, unconfined glacial drift aquifers and does not extend into the deeper sandstone unit. The upper aquifer is commonly used as a drinking water source in the region.
EPA conducted a Remedial Investigation (RI) in 1985 to determine the nature and extent of arsenic contamination in the ground water in Southeastern North Dakota. This RI identified several ground-water wells that exceeded the Safe Drinking Water Act (SDWA) Maximum Contaminant Level (MCL) for arsenic, which, at the time, was 0.05 milligrams per liter (mg/L). The RI attributed the elevated arsenic levels to be from historical use of arsenic-based grasshopper bait and from naturally occurring arsenic in the soils.
Once the RI was completed, EPA conducted a Feasibility Study (FS) to evaluate
options, or remedies, to protect human health and the environment in the areas
identified in the RI where the arsenic contamination was not only naturally
occurring but could be attributed, at least in part, to the bait application
or storage.
The remedy for the Arsenic Trioxide site provided for the expansion of three water treatment plants, approximately 300 miles of water distribution pipeline, additional water storage reservoirs and tanks, and additional water supply wells. The remedy was completed in June 1993, and the site was removed from the National Priorities List (NPL) in July 1996. Remedial actions were taken at the site to address arsenic concentrations in ground water, which serves as the primary drinking water source in the region. At the time of the remedy, the Safe Drinking Water Act Maximum Contaminant Level (MCL) for arsenic was 0.05 mg/L, which was exceeded in the drinking water at the site.
The recently-finalized arsenic rule, which changes the standard from .05mg/L to .01 mg/L prompted an EPA review in June, 2003. That review determined that the remedy is no long protective of human health.
EPA and North Dakota are working to provide safe drinking water for the area's residents.
Site Risk
The area's residents are subject to increased health risk due to exposure to arsenic above the Maximum Contaminant Load (MCL) in drinking water supplies.
| Media Affected | Contaminant | Source of Contamination |
| Drinking water | Arsenic | Historical use of arsenic-based grasshopper bait and naturally occurring (background) levels of arsenic. |
The Safe Drinking Water Act Maximum Contaminant Level for arsenic has been reduced to .01mg/L. This change became effective in January, 2006.
Once the RI Update is complete, EPA and the State will determine what additional RD/RA -Phase 2 work may be needed to be protective. A Cooperative Agreement is being prepared between EPA and the State to share the cost of the RA. EPA will pay 90 percent of the Phase 1 work which is estimated to be approximately $8 million.
Cleanup Progress
The remedy to supply drinking water to meet the arsenic MCL of 0.05 mg/L was completed in June 1993. The site was removed from the NPL in July 1996. The second five-year review was conducted early because of a change in the arsenic MCL, lowering it to 0.01 mg/L effective in January 2006. The Five-Year Review - Document Body (800 KB, PDF file) and Five-Year Review Attachments (2 MB, PDF file, LARGE!) are available online. EPA is working with the state of North Dakota to identify alternatives to provide drinking water that meets the new arsenic standard.
The next five-year review will be completed by September, 2013. More about EPA's regualtion of arsenic in drinking water from EPA HQ.
Community Involvement
Public comment is solicited for five-year reviews.Site Documents
2008 Five-Year Review (PDF, 8.5 MB)2008 Five-Year Review attachments (PDF, 11 MB)
Federal Register Deletion July 5, 1996 (PDF, 2 pp, 193K)
Records of Decision (RODs) List
Contacts
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EPA Frances Constanzi |
North Dakota Carl Anderson |
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View Documents at: |
